Method of and arrangement for controlling the steam temperature in steam power operations with one or more intermediate superheating stages



Dec. 3, 1968 K. KNIZIA 3,413,398

METHOD OF AND ARRANGEMENT FOR CONTROLLING THE STEAM TEMPERATURE IN STEAM POWER OPERATIONS WITH ONE OR MORE INTERMEDIATE SUPERHEATING STAGES Filed Feb. 27, 1967 3 Sheets-Sheet 1 Dec. 3, 1968 K. KNIZIA 3,443,303

METHOD OF AND ARRANGEMENT FOR CONTROLLING THE STEAM TEMPERATURE IN STEAM POWER OPERATIONS WITH ONE OR MORE INTERMEDIATE SUPERHEATING STAGES Filed Feb. 27, 1967 5 Sheets-Sheet 2 I 3P 69 '32 I 1 I 25 67 1 58 i 76 I 42 23" g) I i F 24 63 i 27 I -73 i ,7? ,1; 1 I f9 K. KNIZIA Dec. 3, 1968 METHOD OF AND ARRANGEMENT FOR CONTROLLING THE STEAM TEMPERATURE IN STEAM POWER OPERATIONS WITH ONE OR MORE INTERMEDIATE SUPERHEATING STAGES Filed Feb. 27. 1967 5 Sheets-Sheet 5 @5 w x 3 M74, 4/ M? EM Q: M w W. 4W0, w. H E

ILIZ'II 3,413,808 METHOD OF AND ARRANGEMENT FOR CONTROLLING THE STEAM TEMPERA- TUlRE m STEAM POWER OPERATIONS WITH ONE OR MORE INTERMEDIATE SUPERHEATING STAGES Klaus Knizia, Nochen uber Engelslrirchen, Germany,

assignor to L. & O. Steinmuller G.rn.b.I-I., Gummerskirchen, Germany Filed Feb. 27, 1967, Ser. No. 618,825 Claims. (CI. 60-67) ABSTRACT OF THE DISCLOSURE Power plant in which steam from a boiler is supplied to an auxiliary turbine and exhaust steam from the auxiliary turbine is passed through a superheater to a main turbine while steam bled off from between the inlet of the auxiliary turbine and the inlet of the superheater is expanded to a cooler temperature or is used to generate secondary steam and which expanded steam or secondary steam is also supplied to the superheater inlet.

The present invention relates to steam power operations with one or more intermediate superheating stages. With operations of this type it is necessary to employ control methods which will permit to maintain the live steam temperature as well as the exit temperatures of the steam fiow after one or more intermediate superheating stages at the permissible upper values over as wide a load range as possible. These control methods must on one hand equalize the temperature characteristic of the intermediate superheaters which varies with the load and on the other hand must be able to correct changed heat conveying conditions when the boiler is soiled.

Heretofore the following control methods were employed for changing the exit temperature of the steam from the intermediate superheaters by controlling the steam side:

(1) The injection of feed water into a cooler which precedes or is interposed in the intermediate superheater heating surfaces;

(2) The interposition of heat exchangers in which heat is exchanged from the high pressure side to the intermediate superheater side or vice versa.

With the method according to (1) supra, the steam additionally produced by the quantity of injected feed water passes only through the succeeding turbine and since the quantity of steam has not passed through the high pressure portion, it reduces the degree of efiiciency of the operation.

With the method according to (2) supra, with the transport of heat from the high pressure side to the superheater side, the quantity of heat received by the intermediate superheater must be conveyed in the boiler to the heating surfaces at the high pressure side. Consequently, the heating surface on the high pressure side is increased. Furthermore, since the heat exchangers are passed through by steam at both sides, the heat exchangers are large and expensive in conformity with their prevailing low coefiicient of heat transmission.

It is an object of the present invention to provide a control of the steam temperatures at the exit from the intermediate superheaters which will insure a minimum loss.

It is another object of this invention to provide a control of the steam temperatures as set forth in the preceding paragraph, which will improve the regenerative preheating operation to thereby increase the degree of efiiciency of the operation.

nited States Patent 0 "ice These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

FIG. 1 diagrammatically illustrates a process with a simple intermediate superheating stage.

FIG. 2 shows a circuit for a process with twofold intermediate superheating while employing secondary steam producers.

FIG. 3 illustrates a further circuit according to which secondary steam produced in secondary steam producers is added either to the steam producer or flows to the first secondary turbine where it is expanded and then admixed to the steam in the first intermediate superheater for purposes of cooling.

The present invention is characterized primarily in that the control of the intermediate superheater exit temperatures is effected by the addition of steam produced in secondary steam producers by heating bleeder steam withdrawn from the main turbine. According to this method, the intermediate superheater exit temperatures are controlled by varying the gaseous fiows passing through the intermediate superheaters and, more specifically, by the addition of steam the temperature of which is within the range of the saturated steam temperature limit.

The method will now be described in greater detail in connection with three examples respectively outlined in FIGS. 1, 2 and 3.

FIG. 1 shows a process with simple intermediate superheating. The live steam leaves the boiler 1 and passes through conduit 62 into the topping turbine 2. Here bleeder steam is withdrawn through conduit 3 for the uppermost preheating stage, which bleeder steam in the secondary steam producer 4 produces secondary steam and is then condensed in the feed water preheater 5 pertaining thereto. The steam from the exhaust 6 passes through check valve means 7 and conduit 8 to a major extent to the intermediate superheater 11, whereas a smaller portion passes through conduit 9 into the feed water preheater 10 for purposes of preheating the feed water. Here the said smaller portion of the freed steam serves for preheating the feed water and is condensed. The steam which after the intermediate superheating stage in the intermediate superheater 11 enters the after-turbine 21 is there expanded to condensator pressure while with various bleeding stages further quantities of steam are withdrawn for purposes of preheating. The quantity of steam withdrawn at 12 will in the secondary steam producer 13 produce secondary steam which for instance has the same temperature level as the steam leaving the secondary steam producer 4. The steam deheated in the secondary steam producer 13 is in the feed water container 14 made use of for heating up the feed water. The feed water required for the two secondary steam producers 4 and 13 is withdrawn through a conduit 16 from a feed Water pump 15 at a bleeder station pertaining to the selected pressure. Conduit 16 branches out into two conduits 66 and 76 of which the first branch conduit 66 leads to the secondary steam producer 4, whereas the second branch conduit 76 leads to the secondary steam producer 13. Behind the secondary steam producers, the steam conducting conduits again unite to a conduit 61 leading into the secondary turbine 17. The secondary steam expands in the secondary turbine 17 and from here conveys its steam into the intermediate superheater entrance conduit 8 through conduit 18 to the feed water container 14 or through conduit 19 and control valve 20, said conduit 19 being branched off from the secondary turbine within a pressure range higher than the intermediate superheater-entrance pressure. In this way, the steam quantities produced in the secondary steam producers 4 and 13 are admixed to the intermediate superheater steam at a lower temperature level and thus contribute to an increase in the flow of medium in the intermediate superheater and by lowering the temperature level to a cooling of the intermediate superheater exit temperatures. When the steam from the secondary turbine 17 is not required for cooling the intermediate superheater steam, it will expand to the pressure which pertains to the feed water container.

When the heat reception in the intermediate superheater is too low, the flow of medium through the intermediate superheater will be reduced by withdrawing steam from the cold intermediate superheater conduit 58 and valve 59 conveying the said steam to the secondary turbine 17 at a pressure level which is below the pressure level at the withdrawing station 19. In said secondary turbine 17 the steam expands up to the pressure pertaining to the feed water container 14. In this instance the temperature of the steam rises which passes through the intermediate superheater, and this increase in temperature is due to the fact that at the same ofier of heat, the flow of medium is reduced. The quantity of steam being withdrawn at 12 will drop because the required bleeder steam for the feed water container comes from the secondary turbine 17.

A further circuit is shown in FIG. 2 for a process with a twofold intermediate superheating stage and the application of secondary steam producers which in part produce steam flows of different pressure stages which are made use of in a multistage pressure turbine 23. More specifically, the control operation is as follows. The bleeder steam which is withdrawn from the topping turbine 2 through a conduit 3 is deheated in a secondary steam producer 4 and is condensed in a preheater 5 pertaining thereto. The steam which is withdrawn at the separating pressure 6 is through a conduit 9 conveyed to the preheater 10 pertaining thereto and is condensed therein. The bleeder steam which during the bleeding after the first intermediate superheating is withdrawn at 12 enters a second steam producer 24 in which two partial flows of different pressure are evaporated and then are condensed in a preheater 25 pertaining thereto. Moreover, from the cold branch (Schiene) of the second intermediate superheating stage steam is withdrawn at 26 which through conduit 63 passes to the preheater 27 where it is condensed. Finally, after the second intermediate superheating stage, once more bleeder steam is withdrawn at 28 which through conduit 73 is conveyed to the secondary steam producer 29 from where it passes into the feed water container 14. Feed water is withdrawn from feed pump 15 from a higher pressure stage through conduit 16 and from a lower pressure stage through conduit 30. Conduit 16 branches at 68 into three conduits 66, 76 and 86. Conduit 86 leads to the high pressure portion of the secondary steam producer 29, conduit 76 leads to the high pressure portion of the secondary steam producer 24, and conduit 66 leads to the high pressure secondary steam producer 4. The steam produced in the high pressure steam producer 4 and in the high pressure portion of the secondary steam producer 24 unite and through conduit 64 are conveyed to turbine 23, whereas the steam produced in the high pressure portion of the secondary steam producer 29 passes through conduit 74 to the turbine 23. The feed water withdrawn from the lower pressure stage of pump 15 is on one hand through conduit 30 conveyed to the low pressure portion of the secondary steam producer 24 and on the other hand is through conduit 60 conveyed to the low pressure portion of the secondary steam producer 29. The steam produced in the lower pressure portion of the secondary steam producer 24 passes through conduit 67 to an intermediate stage of the turbine 23. The steam produced in the low pressure part of the secondary steam producer 29 passes through conduit 77 likewise to an intermediate pressure stage of turbine 23. This steam expands in the multi-stage turbine 23 either to a pressure above the first separating pressure or can accordingly at 31 through control valve 32 be conveyed to the first intermediate superheater 11. In view of the thus effected increase in the flow of medium and the reduction in temperature in view of the secondary steam having cooled to the level of the saturated steam, it is possible to control the intermediate superheater temperature in the first intermediate superheater 11. Similarly, by withdrawing through conduit 33 and valve 34, steam can be conveyed to the second intermediate superheater 35 where it can be employed for controlling the temperature. The steam from the secondary turbine 23 which is not required for the control, will expand either to the pressure pertaining to the feed water container 14 and will through conduit 18 pass into the feed water container 14, or through conduit 69 with control valve 49 will be conveyed to other consumers. In addition thereto, it is also possible to withdraw steam from the intermediate superheaters pertaining thereto and to allow said steam to expand in the second turbine 23 so that at the same available heat of the corresponding intermediate superheaters, the steam temperature can be raised. This method to raise the intermediate superheater temperature, however, becomes thermodynamically less favorable than the operation of the intermediate superheaters at somewhat lower temperatures in conformity with the respective available heat.

FIG. 3 shows a further circuit according to which the secondary steam produced in the secondary steam producers 13 and 37 may selectively be conveyed either to the steam producer 1 at a corresponding level through control valve 38 or may through control valve 39 be conveyed to the first secondary turbine 17 where it is expanded to 40 and then is admixed through check valve 41 and control valve 42 to the steam in the first intermediate superheater 11 at 43 for purposes of cooling. However, instead it is also possible to permit the steam through control valve 44 to fiow to the second secondary turbine 45 and from here at a pressure stage above the second intermediate superheater 35 through control valve 46 at 47 to the second intermediate superheater 35 for purposes of cooling. The not required steam will through conduit 18 and control valve 48 pass to the feed water container 14 or through conduit 69 and control valve 49 to another point of the circuit. The steam discharged from the uppermost bleeder stage at 3 is deheated in the secondary steam producer 4 and is condensed in the preheater 5 pertaining thereto. Similarly, the steam discharged at 26 from the intermediate pressure turbine 21 is partly conveyed through a secondary steam producer 36 to a preheater 27 pertaining thereto in which it is condensed. The steam produced in the secondary steam producers 4 and 36 passes through conduit 61 at 50 into the live steam conduit 68 for the secondary turbine 45 and is conveyed thereto likewise through control valve 51. The partial feed water fiows for the secondary steam producers are for the secondary steam producers 13 and 37 withdrawn from the main feed line 53 at 52 and are conveyed through valves 54 and 57 to the secondary steam producers 13, 37, whereas the partial feed water flows for the second steam producers 4 and 6 are withdrawn from corresponding taps of the feeding pump through conduits 16, '66 and 76 and control valves 55, 56 and conveyed to the secondary steam producers 4, 36.

The control of the intermediate superheater temperatures is so effected that the steam obtained in the secondary steam producers 13 and 37 is through control valve 38 conveyed to the high pressure system 1 where it increases the medium flows when it is not required for cooling one of the two intermediate superheaters. Otherwise, the said steam expands in 17 when it is needed for the first intermediate superheater 11, or in turbines 17 and 45 when it is needed for the second intermediate superheater 35.

It is, of course, to be understood that the present invention is, by no means, limited to the method and arrangements set forth above, but also comprises any modifications within the scope of the appended claims.

What is claimed is:

l. The method of operating a power plant having a boiler and multistage turbine means in the form of auxiliary and main turbine means and superheater means on the inlet side of said main turbine means which comprises; supplying primary steam from said boiler to said auxiliary turbine means, supplying exhaust steam from said auxiliary turbine means via said superheater means to said main turbine means, bleeding steam from a point located between the first stage of said auxiliary turbine means and the exhaust steam outlet of said auxiliary turbine means, supplying the bled ofi steam to secondary steam producer means to produce secondary steam, supplying secondary steam from said secondary steam producer means together with exhaust steam from said auxiliary turbine means to the inlet of said superheater means, and expanding at least some of said secondary steam prior to delivery thereof to said superheater means in a second auxiliary turbine to a pressure in excess of the pressure of said exhaust steam.

2. The method according to claim 1 in which at least some of the exhaust steam from said first auxiliary turbine is bypassed from said superheater means to said second auxiliary turbine.

3. The method according to claim 2 in which said second auxiliary turbine is multistage and said secondary steam producer means comprises a plurality of secondary steam producers and steam is supplied from respective stages of said second auxiliary turbine to respective ones of said secondary steam producers.

4. The method according to claim 2 in which said second auxiliary turbine continuously receives steam from said first auxiliary turbine in an amount sufiicient to permit said second auxiliary turbine to idle, and expanding the remainder of the exhaust steam from said first auxiliary turbine in a third auxiliary turbine to a pressure below that on the inlet side of said superheater means.

5. The method accordnig to claim 1 in which said secondary steam producer means includes a pair of secondary steam producers and said bled off steam is conveyed through said pair of secondary steam producers in succession.

6. The method according to claim 2 in which at least some of the steam from said secondary steam producer means is delivered directly to the inlet of said superheater means.

7. The method according to claim 1 in which said superheater means comprises at least two superheaters in series and said auxiliary turbine means comprises first and second auxiliary turbines and one portion of the steam from said first auxiliary turbine is supplied to the inlet of one of said superheaters and another portion of said steam is expanded in said second auxiliary turbine and is thereafter supplied to the inlet of the other of said superheaters.

8. In a power plant; a boiler, a multistage first turbine receiving steam from said boiler, means for bleeding steam from an intermediate stage of said first turbine, a secondary steam producer connected to receive the steam bled otf from said first turbine and operable to produce secondary steam, a second multistage main turbine, a superheater connected to receive exhaust steam from the final stage of said first turbine and the secondary steam produced in said steam producer and to supply the secondary steam and exhaust steam after superheating to said second turbine, and a multistage secondary turbine interposed between said secondary steam producer and said superheater and in which said secondary turbine the said secondary steam is expanded to a pressure greater than the pressure of said exhaust steam.

9. A power plant according to claim 8 in which the secondary steam is at a lower temperature than said exhaust steam at the inlet side of said superheater.

10. A power plant according to claim 8 in which is included means for diverting exhaust steam from said first turbine away from said superheater and to an intermediate stage of said secondary turbine for expansion therein prior to entry into said superheater.

11. A power plant according to claim 8 which includes at least one other secondary steam producer having its steam outlet connected to the steam outlet of said first mentioned secondary steam producer, and a connection from one stage of said main turbine to said other secondary steam producer for feeding steam to said other secondary steam producer.

12. A power plant according to claim 11 in which feed water preheater means are arranged in series with the boiler to supply water thereto, and means for supplying exhaust steam from said secondary steam producers to said feed water preheater means.

13. A power plant accordin to claim 12 in which said feed water preheater means and said secondary steam producers form a structural unit.

14. A power plant according to claim 8 in which said secondary steam producer comp-rises at least two steam producers formed as a structural unit and passed through by the same bleeder steam in succession.

15. A power plant according to claim 14 in which a boiler feed water preheater is provided and is combined in the same said structural unit and is passed through by the same said bleeder steam.

References Cited UNITED STATES PATENTS 2,991,620 7/1961 Nekolny 73 X 3,083,536 4/1963 Vogler 60-73 3,129,564 4/1964 Brunner 60-7 X MARTIN P. SCHWADRON, Primary Examiner.

CARROLL B. DORITY. Assistant Examiner. 

